Microsporidia are ubiquitous parasites causing infections in insects, fish, and mammals. Recently microsporidia have been demonstrated to infect humans. These organisms cause ophthalmic and gastrointestinal infections, primarily in patients with acquired immune deficiency syndrome. Several genera of human pathogens have been cultivated in cell culture. Currently, there are no data regarding the ability of the human pathogens Encephalitozoon intestinalis and Encephalitozoon hellem to survive under various environmental conditions. Also, there are no reports regarding the effects of disinfectants on spores of these two species. The survival of microsporidial spores after exposure to disinfectants such as chlorine, alcohol, and quaternary ammonium compounds, and environmental conditions such as elevated temperature and dessication will be studied. Cultivation of microsporidia in the shell vial system using various cell lines has been investigated and microsporidia appear to replicate in both fibroblast and epithelial cell lines. Staining methods are being evaluated to detect microsporidial inclusions in infected cell culture after exposure to disinfectants and environmental conditions. A monoclonal antibody produced by Dr. Theodore Nash (LPD, NIAID) has replaced giemsa staining for detection of infected cells. Although the monoclonal antibody makes detection of infected cells easier, the assay is still cumbersome and tedious. In an effort to replace staining of infected cell cultures, a method for quantitation of microsporidial DNA has been developed. This assay utilizes polymerase chain reaction and a europium-labeled DNA probe and is semi-quantitative.